The first post-billion, big tech IPO of the year has opened with a bang. Zscaler, a security startup that confidentially filed for an IPO last year, started trading this morning as ZS on Nasdaq at a price of $27.50/share. This was a pop of 71.9 percent on its opening price of $16, and speaks to a bullish moment for security startups and potentially public listings for tech companies in general.

That could bode well for Dropbox, Spotify and others that are planning or considering public listings in the coming weeks and months.

In its first couple of hours of trading, the stock has held around that price, going as high as $28 and as low as $26.06. We’ll continue to monitor the price as the day continues to see how the stock does, and also hear from the company itself.

Initially, Zscaler had expected to sell 10 million shares at a range between $10 and $12 per share, but interest led the company to expand that to 12 million shares at a $13-15 range, which then moved up to $16 and Zscaler last night raising $192 million giving it a valuation of over $1.9 billion — a sign of strong interest in the investor community that it’s now hoping will follow through in its debut and beyond.

Zscaler is a specialist in an area called software-defined perimeter (SDP) services, which allow enterprises and other organizations to better control how they allow employees to access apps and specific services within their IT networks: the idea is that rather than giving access to the full network, employees are authenticated just for the apps that they specifically need for their work.

SDP architectures have become increasingly popular in recent years as a way of better mitigating security threats in networks where employees are using a variety of devices, including their own private mobile phones, to access data and apps in corporate networks and in the cloud — both of which have become routes for malicious hackers to breach systems.

SDP services are being adopted by the likes of Google, and are being built by a number of other tech companies, both those that are looking to provide more value-added services around existing cloud or other IT offerings, and those that are already playing in the area of security, including Cisco, Check Point Software, EMC, Fortinet, Intel, Juniper Networks, Palo Alto Networks, Symantec (which has been involved in IP lawsuits with Zscaler) and more — which speaks both of the opportunity and challenge in the market for Zscaler. Estimates of the value of the market range from $7.8 billion to $11 billion by 2023.